1. Field of the Invention
The present invention relates to an ink jet printing device using thermal energy to eject ink droplets toward a recording medium.
2. Description of the Related Art
Japanese Laid-Open Patent Application (hereinafter referred to as "OPI Publication") Nos. SHO-48-9622 and SHO-54-51837 disclose ink jet printing devices which apply a thermal pulse to ink filling an orifice to rapidly vaporize a portion of the ink. The energy generated by expansion of the vaporized ink is used to eject an ink droplet from the orifice.
OPI Publication Nos. SHO-48-9622 and SHO-54-51837 describe an ink jet recording device wherein a portion of ink in an ink chamber is rapidly vaporized to form an expanding bubble. The expansion of the bubble ejects an ink droplet from an orifice connected with the ink chamber. As described in the August 1988 edition of Hewlett Packard Journal and the Dec. 28, 1992 edition of Nikkei Mechanical (see page 58), the simplest method for rapidly heating the portion of the ink is by applying an energizing pulse of voltage to a heater. Heaters described in the above-noted documents are constructed from a thin-film resistor and thin-film conductors covered with an anti-corrosion layer for protecting the resistor from corrosion damage. The anti-corrosion layer is additionally covered with one or two anti-cavitation layers for protecting the anti-corrosion layer against cavitation damage.
OPI Publication NO. HEI-6-71888 describes a protection-layerless heater formed from a Cr--Si--SiO or Ta--Si--SiO alloy thin-film resistor and nickel conductors. Absence of protection layers from the heater greatly improves efficiency of heat transmission from the heater to the ink. This allows great increases in print speed, i.e., in frequency at which ink droplets can be ejected.